void main(){
  var student=new Student('小B',31);
}

class Person{
  String name;
  Person(String name){
    print('Person. constructor');
  }
}

class Student extends Person{
  int age;

  //子类构造函数调用父类构造函数(但是super要写在最后！！)
  Student(String name,int age):this.age=age,super(name);
}